Liquid crystal display with negative timing signal and dielectric inversion

Abstract

A liquid crystal display device includes a display element containing a liquid crystal display composition for operating in the twisted nematic mode and a two-frequency matrix-addressing circuit for driving the display element. The liquid crystal composition has a critical frequency f c such that at lower frequencies, the dielectric anisotropy of said composition is positive and at higher frequencies is negative, f c lying between the low frequency and high frequency components in the output of said circuit. The arrangement of the device is such that a selected picture cell in said display element can be turned off by applying the high frequency component of said output. Other embodiments include a device in which a dichroic dye is incorporated in the composition and an embodiment which contains means for detecting the temperature of the liquid crystal composition. The effect of temperature change on the performance of the device is compensated by changing the frequency of one of the components or by changing the voltage of the output from the circuit.

What is claimed is: 
     
       1. A liquid crystal display device for operation in the twisted nematic mode, comprising liquid crystal display means including a matrix of display elements and two-frequency matrix-addressing means for supplying a two-frequency output including a high frequency signal f H  and a low frequency signal f L  for the multiplexed driving of said display elements in said display means, said liquid crystal display means containing a liquid crystal display cell including a nematic liquid crystal material having a critical frequency, f c , intermediate the lower and higher frequency components in said output, the dielectric anisotropy of said liquid crystal material being positive at said lower frequency, f L  and negative at said higher frequency, f H , said matrix-addressing means connected to said display cell and being arranged and constructed for applying thereto said higher frequency component f H  as a timing signal for placing the element in a selected condition and as a data signal for turning said element ON and OFF, said higher frequency data signal being in phase with said high frequency timing signal for placing selected display elements in an ON condition and said high frequency data signal being 180° out-of-phase with said high frequency timing signal for placing the display elements in a selected condition into an OFF condition and applying said lower frequency signal f L  as a timing signal to the non-selected display elements. 
     
     
       2. A liquid crystal display device for operation in the twisted nematic mode, comprising a liquid crystal display cell including a plurality of display elements in matrix array, two-frequency matrix-addressing means for supplying a two-frequency output including a high frequency component f H  and a low frequency component f L  for selective driving of said display elements in said display cell, said liquid crystal display cell containing a nematic liquid crystal material having a critical frequency, f c , intermediate the lower and higher frequency components, f L  and f H , respectively, in said output of said matrix-addressing means, the dielectric anisotropy of said liquid crystal material being positive at said lower frequency and negative at said higher frequency, said matrix-addressing means coupled to said cell for applying to selected display elements said higher frequency component f H  as a timing signal for placing the element in a selected condition and as a data signal for turning said elements ON and OFF, said high frequency data signal being in phase with said high frequency timing signal for placing the selected display element in an ON condition and said high frequency data signal being 180° out-of phase with said high frequency timing signal for placing the selected display element in an OFF and applying said lower frequency signal f L  as a timing signal to the non-selected display elements and means for determining the temperature of said display cell for adjusting the output of said matrix-addressing means for compensating for the effect of temperature change on the performance of the display cell. 
     
     
       3. The liquid crystal display device as defined in claim 2, further comprising means for adjusting at least one of the frequencies f L  and f H  of said output in accordance with the temperature as determined by said temperature-determining means for compensating for the effect of temperature change on the performance of said display means. 
     
     
       4. The liquid crystal display device of claim 2 or 3 further comprises means for adjusting the voltage of said output in accordance with the temperature as determined by said temperature-determining means for compensating for the effect of temperature change on the performance of said display means.